Hallmark of true phonology

It is easy to forget that the words we use everyday are built rather “ingeniously.” They code meanings in a combinatorial way, arranging a limited number of phonetic properties in various combinations (phonetic segments, phonemes) and permutations (syllables, morphemes, words). This method of reuse provides tremendous expressive power and creates the means for developing large and open-ended vocabularies. In the realm of animal communication, it appears to be unique to humankind.

How did it come about? Combinatorial structure is hardly a product of humankind's ingenuity, a cultural invention. It is more likely to have evolved. But how? Is it an idiosyncrasy pre-specified in our genetic endowment for language? Or did performance factors drive language towards phonemically structured signals? If, as Anderson claims, neural reuse is a general principle of brain organization, did perhaps this process play a role in the emergence of linguistic reuse?

On-line speaking

Assuming that phonetic reuse evolved from existing capacities, we are led to ask: What were those capacities? Recent work (Lindblom et al., in press) suggests three factors. The first two identify general characteristics of motor control (not specific to speech). The third highlights expressive needs arising from the growth of humankind's cognitive capacity.

1. 1 Positional control (targets>discrete units).

2. 2 Motor equivalence (movement trajectories>recombination).

3. 3 Cognitive processes (expressive needs>sound-meaning link>vocabulary size).

Voluntary non-speech motions are output-oriented, that is, organized to produce desired results in the subject's external environment. So is speech. Experiments indicate that speech movements are controlled by commands specifying a series of positions (targets) in articulatory space. Goals can be attained from arbitrary initial conditions, and the system compensates in response to obstacles and perturbations. Transitions between targets are typically smooth and show stable velocity profiles reminiscent of point-to-point reaching motions. We conclude that speech is in no way special. Both speech and non-speech show positional (target-based) control and motor equivalence (mechanisms for deriving trajectories from arbitrary initial to arbitrary final locations within the work space).

A difference worth pointing out is that, since we speak to be understood, perceptual factors play a role in determining the extent to which targets are reached. But, although information dynamics may modulate the speaker's performance (cf. clear/casual speech), its motor organization is basically the same. Significantly, “target” is a context-independent notion, whereas its associated articulatory movements are highly context-sensitive.

Evo/devo implications

The above account implies that the end-state of phonetic learning is a mastery of targets and motor equivalent trajectory formation. What the learner does in imitating ambient speech is to find the sparsest way of activating the dynamics of the speech effectors. Using a least-action strategy, the child residually ends up with targets.

The context-free nature of target implies that once a target is learned in one context, it can immediately be recruited in another. There lies the key to reuse in the present account. Learning targets speeds up the acquisition process, compared with learning contextually variable movements. For evolution, this means that lexical inventories that are phonemically coded are easier to learn than systems consisting of Gestalt (holistic) sound patterns. Seen in this light, phonetic reuse appears to be an adaptation linked to ease of acquisition. If discrete units are to be derived from positional control and recombination from motor equivalence – two general cross-species motor characteristics – we must ask why other animals do not end up speaking.

This is where the third factor comes in. Humankind's cognitive capacity has developed dramatically from skills not unlike those of present-day apes. It makes it possible to use language to encode a virtually infinite set of meanings. For an account of how that may have happened, see Donald's (Reference Donald1991) synthesis of a broad range of evidence. Donald assumes that, as gestural messages grew more elaborate, they eventually reached a complexity that favored faster and more precise ways of communicating. The vocal/auditory modality offered an independent, omnidirectional channel useful at a distance and in the dark. It did not impede locomotion, gestures, or manual work. The vocal system came to be exploited more and more as the growing cognitive system pushing for lexical inventions and sound-meaning pairs. The reuse capability implicit in discrete targets and motor equivalence conveniently provided the expressive means for these growing semantic abilities to interact in a process of mutual reinforcement. Accordingly, the reason why no other species has extensive reuse lies in the felicitous convergence of all three factors. According to the present account, one would expect reuse not to be limited to the vocal/auditory modality. The formal organization of sign language corroborates that prediction.

Neural reuse: Organizational principle or widespread phenomenon?

While it may be the case that true phonology is uniquely human, combinatorial reuse is known to occur in other domains. Studdert-Kennedy (Reference Studdert-Kennedy and Tallerman2005) draws attention to the work of Abler (Reference Abler1989) who “recognized that a combinatorial and hierarchical principle is a mathematically necessary condition of all natural systems that ‘make infinite use of finite means’, including physics, chemistry, genetics, and language. He dubbed it ‘the particulate principle’.” (Studdert-Kennedy Reference Studdert-Kennedy and Tallerman2005, p. 52).

I take the word “principle” here to be used descriptively, rather than as referring to the possibility that there is a hidden abstract formal condition to be discovered which can be used for explaining all instances of combinatorial and hierarchical coding. In other words, each case of reuse is likely to have its own history.

Which takes us back to neural reuse. If the central nervous system (CNS) exhibits massive reuse of neural circuitry, we may, as Anderson does, choose to talk about a fundamental organizational principle of the brain. Or we might prefer saying that massive reuse of neural circuitry is a widespread phenomenon, bearing in mind that every example of reuse may have its own story.